We conducted molecular dynamics simulations of Si–C alloy to understand the atomistic behavior of solute C atoms near the melt surface and to estimate the surface tension. The surface tensions of liquid Si and C were first evaluated and compared with experimental values and those for other metals. The composition dependence of the surface tension of Si–C alloy was then evaluated, and compared with estimates obtained using the modified Butler’s model. The behavior of C atoms at the surface of liquid Si–C alloys is also discussed.